How to make non-drinkable seawater drinkable?

Question

I've read about desalination and reverse osmosis systems on the large scale, but sounds like it's complex, very energy-intensive and expensive process.

But how can you make it on a smaller scale e.g. at home? Are there any life hacks?

Answer 1

Quite a simple method that would get rid of any salt in the water is to simply boil the water and collect the condensed water vapor in a separate cup / container.

Things you would need:

• Saucepan with a lid
• A clean glass / Pyrex cup or jug
• Sea / salt water
• A stove or fire

Steps to 'de-saltify' the water:

• Place the cup in the middle of the saucepan (or wherever the highest point on the lid of the pan is) you will need to have a small enough glass that will fit in the pan with the lid on!
• Pour in your seawater - try not to go to close to the rim of the pan to avoid spillage, and also avoid making it close to the height of you glass as this might cause sea water to enter which will contaminate the new fresh water
• Place the pan / cup / water combo onto a stove or a sturdy grill above a fire (hot enough to boil water) and apply heat
• Place the lid onto the pan and wait!

How it works:

• The heat from the flames will cause the seawater to boil and thus evaporate, salt in the water is too heavy to evaporate with the water so is left behind.
• The water vapor then rises up in the pan until it reaches the lid where it tries to escape and heads to the highest point of the pan.
• Here it will be unable to escape and will condense as the lid will be cool enough to bring the vapor below boiling temperature and the condensed water will fall into the glass below leaving you salt-free water!

I managed to find a site that explains it in a different way that might be more clear and comes with some fun videos if that gets your blood pumping, here: WikiHow

Note: You will have to try and keep the lid down as the pressure might cause it to bounce around and allow some of the steam to escape!!!

Note 2: This will not disinfect the water if you are actually getting it straight from the sea there will be lots of bacteria in the water which won't be eradicated by this simple process - hence the super expensive purification process in your examples!!!

Answer 2

One of the simpler systems involves gravity fed filtration, often with sand and/or coal as the filter medium. Using a three container construction, you put salt water in the top container. It drips into the middle container that holds your filtration media (sand, coal, etc.). The last container catches the filtered water. (You can simplify the system to a two container system by including the filtration media at the bottom of the top most container.)

Some downsides to this process:

• It doesn't get everything.
• It is slow.
• It requires changing your filtration media frequently.
• You have to drip the water at a rate fast enough to allow gravity to pull it down, but not so slowly that the water evaporates.

Answer 3

This isn't really a hack - but if you really want to do home desalination then there are some practical solutions.

Ocean-going boats have desalination pumps for providing their fresh water. They refer to them as a "watermaker". A quick look on ebay yielded one for c.3000USD.

There's a hand-operated version that they put in life-raft. Not cheap:

http://www.nitro-pak.com/katadyn-survivor-06-desalination-watermaker

...but again on ebay for about 100USD.

There a thing called a "solar distiller" that I think they also use in liferaft. Can't find a price at the moment but they are very basic so should be dirt-cheap.

EDIT:

The only way to save on the huge energy requirements of desalination is to use solar power.

Aside from the small inflatable solar distillers that I mention above, I also remember seeing a very hacky thing done on TV many years ago. The guy dug a pit in the ground about 20cm deep and lined it with black plastic. He the erected what I can only describe as a "tent" of clear plastic over the pit but in such an arrangement that a plastic gutter ran along the bottom edge of the sloping sides into a collector. The water evaporates due to energy absorbed by the black liner and leaves ALL contaminants in the pit. It condenses on the slopes and runs into the gutters and thence into your collector. Voila - fresh drinking water from any contaminated source you can find - for free.

The downside is that you have to regularly flush-out the bottom of the pit. I'm sure a bit of ingenuity could eliminate that step by making it automatically flush itself on a regular basis. For example, I've envisaged a long, shallow sloping bed with a poly-tunnel roof over. Dirty water continually trickles in at the top and evaporates, the residual water continues down the slope and out to waste.